Two weeks ago, Jack Dongarra flew to Changsha, China for a meeting with researchers at the National University of Defense Technology, home to the countryâ€™s top supercomputing program. He expected an update on their plans for a new mega-machine, but they had a little surprise for him: The system was already up and running.

Itâ€™s called Tianhe-2, and with more than 3 million processor cores, itâ€™s the worldâ€™s most powerful supercomputer. It can perform more than 30 quadrillion calculations per second, easily dwarfing the runner-up, an Oak Ridge National Laboratories machine known as Titan. The Oak Ridge system can do 17.59 quadrillion calculations per second, according to its most recent published benchmarks....